A three-dimensional stack memory includes a stack film having conductive films that function as word lines (that is, control gates) of memory cells and insulating films alternately stacked, memory holes passing through the stack film, and MA(O)NOS structures placed in the memory holes, respectively. A part of the stack film is a stepped portion processed in a stepped shape. Contact electrodes that connect the conductive films in respective steps of the stepped portion to upper wires are provided on the steps.
A dry etching technique called resist slimming is known as a technique to form the stepped portion. In the resist slimming, each time an exposed portion of the stack film is ground by one step by dry etching using a resist as a mask, the resist is diminished in an extension direction of the word lines by the dry etching. A newly exposed portion including the previous exposed portion is then ground by one step using the diminished resist as a mask. Such diminishment of the resist and etching of the stack film using the diminished resist as a mask are repeated to obtain the stepped portion.
However, it is conventionally difficult to ensure dimensional accuracies in the respective steps of the stepped portion in the extension direction of the word lines due to a factor such as variation in the elimination amount of the resist in the resist slimming. Because it is difficult to ensure the dimensional accuracies in the respective steps of the stepped portion, positional accuracies in the contact electrodes on the respective steps are hard to ensure. Accordingly, there is a risk that a contact electrode provided on a lower step is brought into contact with a conductive film of an upper step and thus upper and lower conductive films are short-circuited, which leads to a lower yield ratio.